"TURBINE WITH A TUBE CONNECTED DOWNSTREAM"

Abstract

The use of turbines or turbine-generator assemblies to generate electric power has so far required that the tubes disposed downstream thereof, for example suction tubes, are completely submersed in the downstream water. In order to allow for the operation with low or no water level downstream of the turbine using a subsequent tube, the invention discloses a turbine or a turbine-generator assembly, especially a module of such turbine-generator assemblies, which is provided with a means which can at least partially prevent a flow separation from the tube so that the turbine can be operated with an excellent efficiency even when the tube is not completely submersed in the downstream water but leads partially or even completely to the exterior.

Full Text

The present invention relates to a turbine or a turbine-generator unit having a tube connected to the turbine downstream for operation with a liquid level which is low or absent downstream of the turbine, and a turbine-generator module comprising a number of turbine-generator units of this type. The invention also claims the use of a turbine or turbine-generator unit of this type and a method for operating a turbine or turbine-generator unit through which liquid can flow, a method for operating a plant for generating electrical energy, a method for converting a structure for retaining a liquid medium into a device for generating electrical energy, and a method for generating electrical energy at a structure for retaining a liquid medium.
A tube, generally a suction tube, of a turbine or turbine-generator unit in practice always has to open out into the tailwater and must never spray into the open air, since if it does so, particularly in the case of suction tubes with a considerable divergence, the discharge jet can become detached from the suction tube, which reduces the hydraulic efficiency and therefore also the plant efficiency of a turbine-generator unit of this type considerably, to an economically unacceptable level. For this reason, it is attempted to avoid such a situation in practice.
For design reasons, and in this context in particular when existing dam structures are being used, it is, however, sometimes not possible to satisfy this condition, since the tailwater level is too low from the outset. Therefore, in a plant of this type it has hitherto been impossible to install an efficient turbine or turbine-generator unit for generating electrical energy.

Therefore, the object of the present invention is to provide a turbine or turbine-generator unit which can be operated with high hydraulic efficiency even if its tube connected downstream does not open out into the tailwater or does so only partially and which can nevertheless be constructed very efficiently and with a simple design.
According to the invention, this object is achieved through the fact that there is a means which can at least partially prevent the flow from becoming detached from the tube. A means of this type prevents the flow from becoming detached in the tube of the turbine or turbine-generator unit which is connected to the turbine and thereby prevents a drop in the hydraulic efficiency. The plant efficiency, which is composed of the mechanical efficiency, which is substantially determined by friction losses in the bearings, the hydraulic efficiency, which is substantially determined by the turbine efficiency, and the electrical efficiency of the generator, can as a result likewise be kept at a high level, which is extremely important for economic reasons.
Therefore, a turbine or turbine-generator units of this type can be used even if, for example for design reasons, it is not possible for the tube to open out completely into the tailwater, as has hitherto been required. This makes it possible to retrofit even existing dam installations with a liquid level which is low or absent downstream of the turbine with turbine-generator units for the generation of electrical energy without the design of the dam installation itself being altered.
The inventive concept can be used very particularly advantageously for turbines with suction tubes, since in practice, mostly for efficiency reasons, the tube

used is generally a suction tube, and in this case the phenomenon whereby the flow through the divergent suction tube becomes detached, in particular in the case of strongly divergent suction tubes, leads to problems particularly frequently.
For space reasons, it is often expedient for the turbine to be designed with axes of rotation which are substantially horizontal or inclined with respect to this horizontal, in which case the turbine advantageously has a turbine rotor, on which a plurality of turbine blades which are arranged rigidly on the turbine rotor are arranged, resulting in an arrangement which is particularly simple to implement.
A very simple and, at the same time, very effective means for preventing the flow of liquid from becoming detached is a flow body. A flow body of this type is simple to produce and is very simple to implement in design terms.
The efficiency of the flow body can be increased if it is arranged in the tube, preferably in the region of the downstream end of the tube. The phenomenon of the flow becoming detached generally starts at the end of the tube, and consequently the flow body is advantageously also used at that location.
A very particularly simple embodiment without any loss of efficiency results if the flow body is designed as at least one rib which can be arranged substantially horizontally, vertically or also with any desired inclination. A rib, i.e. in principle a simple piece of sheet metal, can be produced and installed particularly easily and effectively.
If a plurality of ribs are used, the distance between two ribs can be calculated substantially according to the formula (Formula Removed), where v is the flow velocity, g is
the acceleration due to gravity and h is the distance

between two ribs. This likewise results in a simple method for predetermining the number of ribs required.
To increase the effectiveness of the flow body still further, it is also conceivable for a rib to be arranged inclined with respect to the flow, so that a local nozzle effect, which makes it significantly more difficult for the flow to become detached, is produced in part of the suction tube.
A further highly advantageous embodiment of a flow body is a pear-shaped body which is arranged concentrically in the tube and is held in the tube by a number of supporting blades. A body of this type is likewise simple to produce and is favorable and simple in design terms to implement.
The most simple design, making it highly advantageous, is an arrangement in which the tube, in the operating position, in the state in which there is no medium flowing through it, at least partially opens out into the open air, so that there is no need for any expensive linings or similar structures.
The advantage of a turbine according to the invention becomes particularly apparent in installations where the tube, in the state in which there is no medium flowing through it, in its operating position, with respect to the tailwater level, projects entirely into the open air, although intermediate ranges of between 25%, 50% and 75% coverage are also conceivable. Dam installations of this type can now, for the first time, be used to generate electrical energy without any restriction to the hydraulic efficiency.
A turbine or turbine-generator unit according to the invention is advantageously used in a turbine-generator module, comprising a plurality of turbine-generator

units which are arranged next to and/or above one another and are connected to one another, for operation with a liquid level which is low or absent downstream of the turbine-generator unit. In a particular design variant, the tubes of the turbine-generator units which are arranged next to one another in a row at least in part open out into the open air, and the means for preventing the flow from becoming detached acts on all the tubes in this row.
For design reasons and/or cost reasons, it is also conceivable to provide a single tube for a number of turbine-generator units of the turbine-generator module. Therefore, under certain circumstances, the turbine-generator module can be more compact, more lightweight and of simpler design.
A turbine, turbine-generator unit or turbine-generator module according to the invention can very particularly advantageously be used in an at least partially existing dam installation with a tailwater level which is low or absent, since in this case no design changes or only insignificant design changes have to be made to the dam installation for the concept to be usable. The turbine-generator module is particularly advantageously operated for generation of electrical energy between two stationary structures of the dam installation, so that the existing structures can be optimally utilized.
The inventive concept of maintaining the flow in the tube of the turbine allows such a turbine to be operated as a result of the flow of the liquid immediately downstream of the tube, at least in sections, being maintained above the tailwater level, so that the hydraulic efficiency of the turbine which is required for energy generation is achieved, it being possible for the flow to be maintained in a very wide

range from 10%, 50%, 100%, 300% and even more than 500% above the liquid level.
A turbine-generator unit according to the invention or a plant for generating electrical energy having at least one turbine-generator unit or at least one turbine-generator module can, for the first time, be operated particularly favorably without any loss of efficiency even if the liquid level at a distance downstream of the tube is kept in a range from below the bottom edge of the tube to at most directly below the top edge of the tube, the flow in the tube being at least partially prevented from becoming detached.
With a turbine, turbine-generator unit or turbine-generator module according to the invention, it is for the first time possible for a structure for retaining a liquid medium to be converted in a particularly simple and advantageous way and without losses of efficiency into a device for generating electrical energy as a result of the level of the medium downstream of the structure and the level of the medium upstream of the structure, which is higher than the level of the medium downstream of the structure, being determined, at least one turbine-generator module being produced, the design and efficiency of the turbines and/or generators being matched to the levels which have been determined, and the flow of the medium immediately downstream of the tube, at least in sections, being maintained above the level of the medium downstream of the structure, by the flow being at least partially prevented from becoming detached from the tube, so that the hydraulic efficiency of the turbine which is required for energy generation is achieved.
The same is true of a method for generating electrical energy at a structure for retaining a liquid medium, the medium having a level which is low or absent downstream of the structure.

The invention will now be described below with reference to the exemplary, non-limiting Figures 1 to 7, which show specific exemplary embodiments. In the drawing:
Fig. 1-4 each show a front view and a side view of a
turbine-generator unit with suction tube in a number of
design variants,
Fig. 5 shows an example of a dam installation having a
turbine-generator module,
Fig. 6 shows a design variant with an external flow
body, and
Fig. 7 shows a design variant without an independent
tube.
Fig. 1 shows a turbine-generator unit 1 in its operating position, having a generator 2 and a turbine 3 which drives the generator 2. The flow through the turbine-generator unit 1 is indicated by the two arrows. A divergent suction tube 4, which opens out into a tailwater UW, is connected in a known manner to the turbine-generator unit 1. In this example, however, the tailwater level UW is below the top edge of the suction-tube opening M, and accordingly, in the state in which there is no medium flowing through it, the suction tube 4 opens out partially into the open air. In order now to prevent the discharge jet 7 from becoming detached from the suction tube 4, as indicated by the dashed line, which, as is known, would considerably reduce the efficiency of the turbine-generator unit 1, a means for preventing the flow in the suction tube 4 from, becoming detached, in the form of a horizontal rib/5,/ is arranged in the opening region of the suction tube 4. As can be seen from the side view, in this case the rib 'b^ extends over the entire width of the suction tube 4. As a result, the discharge jet 7 is discharged over the entire cross section of the suction tube 4, even though the opening

region of the suction tube 4 is not completely covered by the tailwater UW, as is required in conventional arrangements.
As an alternative to a suction tube 4 as shown in Fig. 1, which is characterized by a divergent change in cross section, it is also possible to use a simple tube of any desired cross section. Arrangements of this type are well known and it is therefore also known that in arrangements of this type a lower efficiency has to be accepted from the outset. Experience has shown that with divergent suction tubes hydraulic efficiencies of >80% can be achieved, whereas with simple tubes efficiencies of typically
Of course, the flow bodies according to the invention are also equally suitable for turbines with tubes connected downstream, such as for example suction tubes, without generators, for example in installations where the turbines drive a generator arranged elsewhere via suitable means.
Fig. 2 now shows the same turbine-generator unit 1 with suction tube 4 as that shown in Fig. 1. However, in this example the discharge jet 7 sprays out completely into the open air, i.e. in the operating position the tailwater level UW is below the bottom edge of the suction-tube opening M; in extreme cases, there would even be no liquid level at all downstream of the turbine or tube. In order once again to prevent the flow from becoming detached, with all its negative consequences, in this exemplary embodiment there are two horizontal ribs 5, arranged one above the other, as

flow bodies, but in this case they do not extend over the entire width of the suction tube 4. By way of example, the ribs 5 can be arranged in such a way that the relationship (Formula Removed) where v is the flow velocity,
g is the acceleration due to gravity and h is the distance between the two ribs, is satisfied. Moreover, in this case one of the ribs 5 is additionally in part also arranged inclined with respect to the flow passing through the suction tube 4, which likewise improves the efficiency of the ribs 5.
Figure 3 shows a further exemplary embodiment of a turbine-generator unit 1. In this case, the suction tube 4 changes from a round cross section in the turbine region into a rectangular or, as in this case, square suction-tube opening M, as is generally the case in practice. In this example, the rib 5 is arranged vertically.
Of course, the ribs 5 can be in any desired arrangement and can of course also be of any desired form, for example may be in the form of an airfoil or a simple cuboidal shape, provided that the desired effect, namely that of preventing the flow from becoming detached in the suction tube, is achieved as a result. Of course, ribs 5 which are arranged rotated through any desired angle about the longitudinal axis of the turbine-generator unit 1, such as for example diagonally arranged ribs 5, or any desired mixture of horizontal, vertical and rotated ribs 5, are also possible, and these ribs may, of course, also be of any desired length, may extend over part or all of the width of the suction tube 4, and if necessary, as shown in Fig. 2, may also be positioned at an inclination.
Fig. 4 now shows a further possible way of preventing the flow in the suction tube 4 from becoming detached. In this example, the divergence of the suction tube 4

of the turbine-generator unit 1 is produced only by the change in cross section over the length of the suction tube 4. In this case, the round cross section in the turbine region merges into a square cross section at the suction-tube opening M, the side length of the square corresponding to the diameter of the suction tube 4 in the turbine region, which corresponds to the most compact arrangement of a turbine-generator unit 1 with suction tube 4. The flow body provided in this case is a concentrically arranged, pear-shaped body 6 in the opening region of the suction tube 4, which is held in the suction tube by two supporting blades 8. However, the supporting blades 8 could also be designed as ribs 5 as shown in the embodiments illustrated in Figs. 1 to 3, so that they also, at the same time, function as an additional flow body.
The required axial extent of the flow bodies is substantially dependent on the divergence or length of the tube, on the flow velocity of the liquid medium and on the height of the tailwater level UW or the level difference between the top water and tailwater UW and can be adapted to match the specific conditions. However, practical tests have shown that flow bodies in the region of the opening, i.e. approximately in the final third of the tube, are sufficient.
It will be clear that it is impossible to list all the possible embodiments and combinations of suitable flow bodies in the opening region of the tube. What is essential for the invention, as is clear from the description, is the effect of these flow bodies rather than their precise configuration. In particular, the present application encompasses all possible embodiments of flow bodies of this type.
Now, Fig. 5 shows part of a dam installation 12 having a number of stationary structures, in this case piers

11, between which a turbine-generator module 9, comprising a number of turbine-generator units 1 arranged next to and/or above one another with longitudinal axes which are slightly inclined with respect to the horizontal, is arranged. A turbine-generator module 9 of this type may also be arranged in such a manner that it can be raised and lowered, in which case a lifting device, e.g. a crane, which is not shown, may be provided in order to raise and lower the module, and the turbine-generator module 9 may be guided in a guide 14, which is only indicated in the figure. The dam installation 12 shown here also has a rotatably mounted weir gate 10 which can be closed if necessary, for example in situations in which the turbine-generator module 9 is being raised. The dam installation 12 is generally used to maintain a certain top water level OW, the tailwater level UW either being a natural result or also being controllable.
In the example shown in Fig. 5, the weir crest 13 of the dam installation 12 is so high that the suction tubes 4 of the upper row of the turbine-generator units 1, in their operating position, spray partially into the open air, and in this example the tubes of the upper row of the turbine-generator units 1 do not open out completely into the tailwater UW, as indicated by the dashed line. By using a flow body as described in Fig. 1 to 4, these turbine-generator units 1 can now also be used in dam installations 12 of this type, which would hitherto have only been possible with in some cases very considerable losses in efficiency. Furthermore, the turbine-generator module 9 may comprise closure devices (not shown here), by means of which some and/or all of the turbine-generator units 1 can be closed off so that the liquid cannot flow through the turbine-generator units 1. This situation could arise, for example, if the top water level OW becomes too low and the damming function of the dam

installation can no longer be ensured, the turbine-generator module 9 is being raised out of the waterway for maintenance or in the event of a flood or in order to control the quantitative flow.
A situation of this nature, in which the tailwater level UW is very low or absent altogether, may arise in particular in existing dam installations 12 which have hitherto only been used to maintain a predetermined liquid level and are now also to be used to generate electrical energy. Hitherto, converting dam installations 12 of this type into installations for generating electrical energy has been impossible or has involved very considerable levels of outlay, since conventional tubes, such as for example suction tubes 4, which spray completely or partially into the open air would mean a considerable loss of efficiency, which would in turn make the installation uneconomical. By using the flow bodies according to the invention it is now possible for the first time for even existing dam installations 12 of this type to be converted into installations for generating electrical energy with an acceptable level of outlay.
For this purpose, by way of example, closure members which are present between two piers 11 are replaced by a turbine-generator module 9 as illustrated for example in Fig. 5. The turbine-generator module 9 can be matched to the predetermined levels and the existing structures of the dam installation 12, so that an optimum efficiency can be achieved. The suction tubes 4 of the turbine-generator units 1, which open out at least partially into the open air, are equipped with flow bodies according to the invention, so that the flow does not become detached in the opening region of the suction tubes 4 and the full efficiency can be exploited.

Fig. 6 also shows a further possible exemplary embodiment of a turbine-generator unit 1 with a generator 2 and a turbine 3, to which a short suction tube 4 is connected. In this case, a means for preventing the flow in the suction tube 4 from becoming detached is arranged directly downstream of the suction tube 4, as seen in the direction of flow. In this specific example, this means comprises a horizontal rib 5, which is held in the flow of the discharge jet 7 by a supporting construction 15. This example shows in particular that the means does not necessarily have to be arranged in the suction tube 4 or tube, but rather may also be located outside it.
In the examples shown in Fig. 1 to 6, the turbine housing in which the turbine 3 runs and the tube connected to the turbine 3 are separate components which, as indicated in Fig. 1 to 6, are connected to one another, for example by means of a flanged connection. It can now be seen from Fig. 7 that the tube does not necessarily have to be an independent component, but rather it is also possible for the turbine housing 16 to be widened into the shape of a tube at the downstream end, and of course also into the shape of a suction tube, so that it fulfills the same function as a separate, connected tube. Of course, as described above, it is then possible for a means for preventing the flow in the tubular widening from becoming detached, such as for example in this case two ribs 5 which are rotated with respect to the horizontal or vertical, to be arranged in this tubular widening of the turbine housing.
Even if the exemplary embodiments only show variants with divergent tubes or tubes with a constant cross section, other tubes, such as for example a convergent tube (= a tube with a decrease in cross section) or an

alternately divergent, convergent or constant tube, are also of course, conceivable.
The turbine 3 with a tube 4 and a means 5 for preventing the flow through the tube 4 from becoming detached from the tube 4 can for example be arranged in a dam installation 12 or in an at least partially existing dam installation 12, like a weir installation or a lock, with low or absent tailwater level UW for the generation of electrical energy. The turbine 3 is preferably operated between two stationary structures 11 of the dam installation 12 in order to generate electrical energy.

WE CLAIM:-
1. A turbine having a tube which is connected to the turbine
downstream, wherein, for operation with a low or absent liquid level
downstream of the turbine, characterized in that there is provided a
means (5) which can at least partially prevent the flow through the tube
from becoming detached from the tube by arranging the means (5) in the
flow in the opening region of the tube (4).
2. The turbine as claimed in claim 1, wherein the tube (4) is a suction tube.
3. The turbine as claimed in claim 1 or 2, wherein the turbine (3) has an axis of rotation which is horizontal or inclined with respect to this horizontal.
4. The turbine as claimed in one of claims 1 to 3, wherein the turbine (3) has a turbine rotor on which a plurality of turbine blades are rigidly arranged.
5. The turbine as claimed in one of claims 1 to 4, wherein the means (5) for preventing the liquid flow from becoming detached is a flow body.
6. The turbine as claimed in claim 5, wherein the flow body is arranged in the tube (4), preferably in the region of the downstream end of the tube (4).
7. The turbine as claimed in claim 5 or 6 wherein the flow body is designed as at least one rib.
8. The turbine as claimed in claim 5, 6 or 7, wherein at least one flow body is arranged horizontally.

9. The turbine as claimed in one of claims 5 to 8, wherein at least one
flow body is arranged vertically.
10. The turbine as claimed in one of claims 5 to 9 wherein at least one flow body is inclined with respect to the horizontal or vertical.
11. The turbine as claimed in one of claims 7 to 10, wherein at least one rib is arranged inclined with respect to the flow.
12. The turbine as claimed in claim 5 or 6, wherein the flow body is designed as at least one pear-shaped body (6) arranged concentrically in the tube (4).
13. The turbine as claimed in claim 12, wherein the pear-shaped body (6) is held in the tube (4) by a number of supporting blades.
14. The turbine as claimed in one of claims 1 to 13, wherein the tube (4) at least partially opens out into the open air.
15. The turbine as claimed in any one of claims 1 to 14, wherein in the state in which there is no medium flowing through the tube (4), 25% or more of the outlet cross-sectional area of the tube (4) in its operating position is above tailwater level (UW).
16. The turbine as claimed in any one of claims 1 to 15, wherein the turbine (3) drives generator (2) to form a turbine-generator unit (1).
17. The turbine as claimed in any one of claims 1 to 16, wherein the turbine (3) is arranged in a turbine-generator module comprising a number of turbine-generator units (1) which are arranged next to and/or above one another and are connected to one another to form one or more modules.

18. The turbine as claimed in claim 17, wherein the tubes (4) of the turbine-generator units (1) arranged in a row next to one another, in the state wherein there is no medium flowing though them, in their operating position based on the tailwater level, open out at least partially into the open air, and the means (5) for preventing the flow from becoming detached acts on all the tubes (4) in this row.
19. The turbine as claimed in claim 17 or 18, wherein at least in some cases a tube (4) is assigned to a number of turbine-generator units (1).
20. The turbine as claimed in claim 17, 18 or 19, wherein there is a closure device (10), by means of which at least one turbine-generator unit (1) can be closed off so that liquid cannot flow through it.
21. The turbine as claimed in any one of the preceding claims, wherein
the turbine is moveably arranged between the two stationary structures
(11) of the dam installation (12) to be raised and lowered between the
stationary structures (11) by means of a lifting device.
22. A method for operating a turbine as defined in any one of claims 1 to
21 through which liquid can flow with a tube (4) which is connected to
the turbine downstream with a liquid level (UW) which is low or absent
downstream of the turbine (3), the flow of the liquid in the downstream
direction being maintained, at least in sections, above the tailwater level
(UW) immediately after the tube (4), by preventing at least partially the
flow from becoming detached from the tube (4), by arranging a means (5)
in the flow in the opening region of the tube (4), so that the hydraulic
efficiency of the turbine which is required for energy generation is
achieved.

23. The method as claimed in claim 22, wherein the flow immediately downstream of the tube (4) is kept at least 10% above the tailwater level.